css/ // our own work with css
extends/ // where we specialized the standard classes
helpers/ // our utility classes
js_addons/ // javascript complements if any
lang/ // scripts to translate
logs/ // some debugging our processing logs
models/ // scripts related to data access (M of MVC)
pages/ // the pages scripts... pages are made of parts
parts/ // where controllers are (C of MVC)
sqlitedb/ // if database type is sqlite, it may be here
templates/ // the design and templates (V of MVC)

Structure of the "tdlist/extends/" directory

extends/Tdl_Extends.php
That's where all F_Something classes become Ef_Something
extends/Tdl_Field.php
Where we define our own specific field types
extends/Tdl_ListViewExtended.php
Where we define our own ways of rendering lists